The present invention relates to electrically operated valves for use in providing a fluid pressure control signal. In particular, the invention relates to electromagnetically actuated valves for providing a variable vacuum signal for use in controlling a fluid pressure servoactuator in response to an electrical control signal.
In automotive engine and accessory control systems, it has been found particularly convenient to employ engine developed vacuum as a source of fluid pressure for operating vacuum servoactuators or motors for various engine control functions. However, as automotive engines have decreased in displacement in the interests of reducing weight and fuel consumption, the amount of vacuum available for accessories has substantially diminished.
Heretofore, on-board vacuum control systems have employed electrically operated control valves which, during periods of control operation, provided for valve actuation between a vacuum supply port and an atmospheric venting orifice in a manner analogous to a single-pole double-throw switch. In such arrangements, an electrical coil moved an armature-valve member between one position opening a vent port and closing a vacuum port and another position closing the vent port and opening the vacuum port. This known valving arrangement thus resulted in a continuous flow of atmospheric air or vent bleed into the engine valving chamber and thus to the vacuum source.
It has also known to employ dual electrical coils for individually actuating a vacuum and vent valve poppet member in response to electrical control signals. Such dual coil valve arrangements have necessarily resulted in bulkiness of the control valve and increased manufacturing costs in providing two electrical coils and the associated electrical connections thereto.
The aforementioned dual coil vacuum control valve, also provides continuous flow of atmospheric air to the valving chamber which reduces the engine manifold vacuum and drains engine power.
Thus, it has long been desired to find a way or means of providing a vacuum control signal in response to an electrical input control signal and provide such a function without causing continuous bleed of atmospheric air into the vacuum source.
Furthermore, it has been desired to provide such a control valve which is electrically operated by a single coil and yet provides a control signal by alternately applying vacuum and venting a control signal pressure chamber without permitting continuous bleed of atmospheric air to the vacuum source.
It is known in the solenoid art to utilize a permanently magnetized armature in association with the magnetic forces generated by current flow in an electrical coil. Examples of such devices are described and shown in the periodical "Machine Design", Volume 52, Aug. 21, 1980 Issue at page 42 published by Penton Publishing Company, Cleveland, Ohio. The use of a permanent magnet armature for an electromagnetically actuated device permits short current pulses to latch the armature. Movement of the armature in an opposite direction for latching is accomplished by short current pulses of opposite polarity.
Thus it has been desired to find a way of using electromagnetic actuation to actuate and hold a control valve for providing a vacuum control signal in response to an electrical signal applied to a single coil and yet provide such control signal without permitting continuous vent flow through the valve to the engine vacuum source.